Self-Assembled Melamine Monolayer on Cu(111)

The self-assembled structure of melamine (1,3,5-triazine-2,4,6-triamine) deposited on Cu(111) was studied under ultra-high-vacuum conditions using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS). Molecular packing and conformation were investigated as a function of the annealing temperature. The molecules deposited at room temperature were found to be aligned with the molecular plane approximately perpendicular to the surface. At around 150 °C, the molecules became aligned in a row-type structure and were all coupled to the Cu(111) surface. At still higher annealing temperatures, a new two-dimensional (2D) network was formed via the polymerization of the adsorbed monolayer of melamine. A multistep model consistent with STM, XPS, and UPS results is proposed, starting with a self-organized vertically adsorbed melamine monolayer and ending with the formation of a 2D network lying on Cu(111) interpreted as a ring-opening polymerization of melamine. The reactive Cu(111) surface is believed to be one of the keys in this multistep reaction.